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Fire adaptive traits of Eucalpyts

Fire plays an important role in shaping the Australian landscape and its flora and fauna. This influence is millions of years old, and is the focus of research led by Professor Emeritus Mike Crisp.

Biomes are defined as large ecological areas housing animals and plants that complement each other and evolve over time. Mike Crisp’s team studied the origins of fire-prone biomes dominated by Eucalyptus trees and wondered whether the predominance of the Eucalypts was related to repeated exposure to fires.

Fires are known to drastically affect landscapes, aided by seasonal changes that create a cycle of growing and burning. This process is thought to have begun after the separation of Gondwana, an ancient supercontinent.

The study showed that the dominance of eucalypts that maintained this grow/burn cycle was likely due to special fire-adaptive traits that started with Myrtaceae, a species related to the Eucalyptus.

Many eucalypts have special fire-adaptive traits, including re-sprouting after fires. This is often referred to as epicormic sprouting, and is very common in eucalypts. After fires, a series of events trigger the sprouting to occur. One way this can happen is if there is damage to the top, or crown of the tree. Hormones suppressing the sprouts may stop being generated by the crown of the tree, causing the sprouting to occur. The buds of these sprouts are often protected by thick bark, which explains how they might manage to survive the intense heat of a bushfire.

To determine when eucalypt-fueled fires began, the researchers managed to trace fire-adaptive traits by creating a phylogeny, or a map of the appearance and evolution of those traits. It’s also possible to determine when fires occurred by tracing a specific kind of charcoal that is only left behind by fires.

The research showed that the trait of re-sprouting appeared 60 to 62 million years ago. This suggests that the areas that are dependent on the renewal brought about by fires existed a lot earlier than was thought before by at least 50 million years.

Due to their ability to re-sprout after fires, it was also noted by the researchers that this puts biomes dominated by the eucalypts in a very good position to act as carbon banks for CO₂, compared to other fire-renewing biomes.

In 2017, we celebrate 50 years of Biology at ANU. This article is one of a set featuring the achievements and memorable occasions of ANU biologists during those first 50 years.
Read more at Biology at ANU – the first 50 years.